1. Field of the Invention
The present invention relates to a numerical control unit for controlling axial movement of a moving section of a machine tool in response to manual axial movement operations.
2. Description of the Related Art
With a well known numerical control unit, if an axial movement operation is performed manually function generation is carried out for each axial control period corresponding to the movement direction, to achieve axial movement control of a moving section of a machine tool. Conventionally, in order to avoid mechanical collisions in a manual axial movement operation, a range in which movement is possible is registered in advance, and when this range is deviated from, control is executed so that a moving section is decelerated and stopped at the boundary of this range.
With a conventional method for preventing collision in manual operation, it is standard for a range in which movement is possible for each control axis to be stored in advance, and there is a problem that it is necessary to avoid collisions of interfering objects that are within the range in which movement is possible for each control axis, such as workpiece, a jig, a tailstock, etc. by an operator taking care in operations.
Also, as a method for automatically avoiding interference between a tool and workpiece using a manual operation, Japanese patent Laid-open No. 2000-84794 discloses a method of adding means for predicting interference. Means for predicting interference added to an external section confirms whether or not there is interference between a tool and workpiece resulting from a manual operation by the operator, and if it is determined that there will be interference an axial stop instruction to be sent to the numerical control device is issued. However, when only a stop command is issued unidirectionally towards the numerical control unit, axial movement is started or restarted very finely while confirming whether or not there is interference, for an axial movement instruction manually by an operator, movement is very fine in order to avoid interference, and it is not possible to decelerate and stop accurately at a desired position.